Recently published work has supported the emerging concept that the vascular and sinusoidal endothelium and, specifically, endothelial nitric oxide synthase (eNOS) localized to this cellular structure play important roles in aspects of the vascular homeostasis and erection physiology of the penis. Investigations of eNOS in the penis have shown that the enzyme is activated by a specific phosphorylation mechanism under blood flow stimulation so that it releases the gaseous messenger molecule nitric oxide (NO) in a steady, continuous manner. This finding indicates that eNOS contributes significantly to NO-mediated penile erection, regulating the penile tumescence and erection maintenance phases of the erectile response. Further investigation has revealed that eNOS is deficient in the penis under various conditions associated with erectile dysfunction including diabetes and aging. These reports correspond with epidemiologic studies that have identified high rates of erectile dysfunction in individuals with cardiovascular diseases, leading to suggestions of a common pathogenic link: endothelial dysfunction. However, the precise mechanisms underlying the putatively defective endothelial function in the penis associated with vasculogenic erectile dysfunction remain poorly understood. It is hypothesized that the actions of eNOS in the penis under the control of various complex regulatory mechanisms have an impact on the endothelial-dependent biological functions of this organ. Accordingly, this research proposal centers on two areas, the investigation of several specific molecular mechanisms controlling eNOS actions in the penis in correlation with physiologic and pathophysiologic events of this organ, and the assessment of "activated" eNOS as a vasculoprotective molecular target for preserving penile vascular function. Specific aims are: (1) to characterize eNOS isoform-specific regulatory mechanisms (i.e., post-translational phosphorylation, protein-protein interactions) operating in the penis during physiologic penile flaccidity and erection in the rat; (2) to determine roles of eNOS isoform-specific regulatory mechanisms in the penis in the pathogenesis of atherosclerosis-associated erectile dysfunction using porcine and rodent animal models; (3) to determine roles of eNOS isoform-specific regulatory mechanisms in the penis in the pathogenesis of age-associated erectile dysfunction in the rat; and (4) to evaluate "activated" eNOS as a molecular target for improving erectile function using select interventions (i.e., growth factor therapy, pharmacoinduction, and gene transfer) in rodent animal models of vasculogenic erectile dysfunction. The work may advance treatments not only for erectile dysfunction, but also for disorders of endothelial dysfunction in general.